1. Field of Invention
This invention relates to compliant substrates that can be used as templates for epitaxial growth. This invention also relates to semiconductor structures including electronic and optoelectronic devices formed on the compliant substrates. This invention further relates to processes for forming the compliant substrates and the semiconductor structures.
2. Description of Related Art
Pseudomorphic epitaxy involves the epitaxial growth of high-quality single crystal thin films on lattice-mismatched substrates. Pseudomorphic epitaxy has found many applications. For example, high-performance lasers utilizing strained InGaAsP quantum wells have been fabricated on InP for telecommunications applications. Unfortunately, lattice-mismatched films cannot be grown beyond their xe2x80x9ccritical thicknessxe2x80x9d limit, which decreases with increasing lattice mismatch, without generating misfit dislocations that seriously impair the performance of devices made from the films. For structures that require thick layers of lattice-mismatched films, such as strained p-i-n photodetectors, a specially prepared substrate must be developed on which to grow the films.
Compliant substrates, that have sufficient mechanical flexibility to comply to the lattice parameter of an epitaxial layer grown on them, have been proposed as a possible solution for growing lattice mismatched films such as GaN on GaAs. In this scheme, the substrate is made to accommodate the lattice preference of the film grown above it, rather than the reverse roles that characterizes typical epitaxial growth. Previous ideas for realizing compliant substrates include using thin, free-standing GaAs membranes, thin silicon films bonded to another substrate through a SiO2 intermediate layer, and intentionally misaligned wafer-fused III-V films. See, for example, Appl. Phys. Lett., vol. 64(14), pp. 1856-1858, 1994; Appl. Phys. Lett., vol. 64(26), pp. 3640-3642, 1994; Appl. Phys. Lett., vol. 69(2), pp. 173-175, 1996; and LEOS ""96, Boston, Mass., paper ThK2, 1996, which are each incorporated herein by reference in their entirety.
Although freestanding membranes are useful for demonstrating the concept of compliant substrates, they are too fragile for practical use.
Wafer bonded films have recently shown great promise as compliant substrates; however, they require cumbersome wafer-bonding and substrate removal steps to fabricate them. See, for example, IEEE J. Quantum Elect., vol. 3, pp. 943-951, 1997, which is incorporated herein by reference in its entirety.
This invention provides compliant substrates that overcome the above-described problems of known compliant substrates.
This invention separately provides semiconductor structures comprising devices formed on the compliant substrates.
This invention also separately provides processes for forming the compliant substrates.
This invention further provides processes for forming the semiconductor structures.
Exemplary embodiments of the compliant substrates according to this invention comprise a first single crystal layer; an amorphous buffer layer on the first single crystal layer; and a second single crystal layer on the amorphous buffer layer. The second single crystal layer is compliant and able to mechanically deform, or comply, to match the lattice parameter of an epitaxial film grown on the second single crystal layer. III-V materials can be used to form the compliant substrates.
Exemplary embodiments of the semiconductor structures according to this invention can comprise various electronic and optoelectronic devices, that include lattice mismatched single crystal layers, formed on the compliant substrates.
Exemplary embodiments of the processes for forming the compliant substrates according to this invention comprise growing an epitaxial laminate of an intermediate single crystal layer between a thin single crystal layer and another single crystal layer. The intermediate single crystal layer is then treated so that it forms an amorphous buffer layer. The formation of the amorphous buffer layer partially xe2x80x9creleasesxe2x80x9d the thin single crystal layer, so that it can comply with an epitaxial film grown on the thin single crystal layer.